February 22, 2006

Tiny, frozen Pluto adds to its moon family

LONDON (Reuters) - The tiny, distant and frozen planet
Pluto, for 30 years believed to have just one moon, has
suddenly been found to have two more satellites.

Only discovered in 1930 because of its vast distance from
Earth, Pluto has remained a largely enigmatic object ever
since.

Some three billion miles from the Sun, Pluto, the ninth
planet, is the only one not yet to have been visited by a
spacecraft.

Its first known satellite Charon was not discovered until
1978. With a diameter of 1,200 km, it is half that of Pluto --
abnormally large for a moon in relation to its primary.

But now, using images from the Hubble Space Telescope,
scientists from Johns Hopkins University, Southwest Research
Institute and the Massachussetts Institute of Technology say
they have found two more tiny orbiting satellites, P1 and P2.

Both are traveling outside the orbit of Charon and are tiny
by comparison, the scientists wrote in the journal Nature.

P1, the more distant of the two from Pluto, has a diameter
of between 60 and 165 km while P2 is 20 percent smaller.

"Although definitive orbits cannot be derived, both new
satellites appear to be moving in circular orbits in the same
orbital plane as Charon with orbital periods of about 38 days
for P1 and 25 days for P2," they wrote.

The discovery of the two new members of Pluto's family make
it the only object in the Kuiper Belt -- a vast region of rock
and ice beyond Neptune which contains debris from the formation
of the solar system -- known to have multiple satellites, the
scientists said.